well if you had got a proper plumber who new how to do electric showers then they could of advised you before spending.
common practise is to check the pressure on your mains before anything else,
which needs to be at least 1 bar. to operate the heating elements micro switch.
if the whole house has low pressure then the man who fitted the combi should of known this.
check with the water company it is their duty to supply you with good pressure.
hi-spec plumbing & heating.
February 2008